1. Field of Invention
The present invention relates to an electro-optical panel, an electro-optical panel module, and a projection display device, and, more particularly, to an electro-optical panel structure suitable for use as a light valve of the projection display device.
2. Description of Related Art
An electro-optical panel for performing light modulation to form a predetermined image is sometimes used in a projection display device such as a liquid crystal projector. Here, a condensing optical system and an enlarging projection optical system are provided. The condensing optical system is provided to cause light from a light source to strike the electro-optical panel. The enlarging projection optical system is provided to project the light that has passed through the electro-optical panel onto a projection surface, such as a screen, and form an enlarged image. The light condensed by the condensing optical system passes through the electro-optical panel, resulting in the formation of the predetermined image, which is projected towards the front by the enlarging projection optical system.
However, when dust sticks onto the outer surface of two transparent substrates making up the above-described electro-optical panel or when the outer surface of the two transparent substrates get scratched, the outer surface of the transparent substrates are brought to a focus, since the outer surface of the transparent substrates are separated from a liquid crystal layer of the electro-optical panel that is brought to a focus by the condensing optical system by only about 1 mm. Therefore, the above-described electro-optical panel has the problem that the quality of a projected image is considerably reduced even when the dust or scratches which get enlarged and projected are only about 10 μm to 20 μm in size.
In the projection display device, the electro-optical panel is irradiated with intense light generated from a light source, so that a localized temperature rise tends to occur in the electro-optical panel. Since such temperature rise changes the light transmittance ratio of some liquid crystals, display quality is reduced. In addition, such temperature rise causes deterioration in electro-optical substances such as the aforementioned liquid crystals.
In view of these problems, Japanese Unexamined Patent Publication Nos. □9-105901 and 9-113906 disclose a technology which increases heat dissipating capability and which prevents dust from sticking onto and scratches from being formed on the outer surface of a transparent substrate of an electro-optical panel. In this technology, another transparent substrate is disposed away from the aforementioned transparent substrate of the electro-optical panel, with an adhesive being used and applied to the outer surface of the transparent substrate of the electro-optical panel. When another transparent substrate is disposed, an air gap is formed between the transparent substrates separated from each other, so that heat dissipating capability is increased. In addition, when another transparent substrate is disposed, it is possible to prevent dust from sticking onto and scratches from being formed on the outer surface of the transparent substrate of the electro-optical panel. However, when this technology is used, another transparent substrate is disposed away from the transparent substrate of the electro-optical panel, so that light is reflected at the interface between the electro-optical panel and the air gap and at the interface between the transparent substrate disposed away from the transparent substrate of the electro-optical panel and the air gap. This results in such problems as loss of a large amount of light, and the necessity of performing an additional step to form a reflection prevention film onto the substrate surfaces in order to prevent reflection of light.
In order to overcome the above-described problems, the present inventor has conducted various studies on methods of adhering a surface of another substrate onto the outer surface of a transparent substrate of an electro-optical panel, using a transparent adhesive. An application of a method based on such studies has already been filed. FIG. 6 is a schematic view of the structure of an electro-optical panel based on this method. In the electro-optical panel, liquid crystals, which are electro-optical substances, are filled and sealed with a sealant (not shown) between an element-formed substrate 11 (having a pixel electrode and an active element formed on the inner surface thereof) and an opposite substrate 12 (having an electrode that opposes the pixel electrode and that is formed on the inner surface thereof) that opposes the element-formed substrate 11. A surface of a transparent substrate 28 is adhered to the outer surface of the element-formed substrate 11 with a transparent adhesive 30, while a surface of a transparent substrate 29 is adhered to the outer surface of the opposite a surface of a transparent substrate 29 is adhered to the outer surface of the opposite substrate 12 with a transparent adhesive 30. However, when this method is used, the transparent adhesives 30 do not allow flexing of the electro-optical panel, and must have refractive indices of light which are substantially the same as those of the element-formed substrate 11, the opposite substrate 12, and the transparent substrates 28 and 29, so that there is a limit as to the kind of adhesive material which can be used. The adhesive material used must have low viscosity and must possess flowing properties to a certain extent after it has hardened. Therefore, as shown in FIG. 6, after the surfaces of the corresponding substrates have been adhered together, the transparent adhesives 30 flow outwardly from adhesion portions between the corresponding substrates. Consequently, during the manufacturing process or after completion of the manufacturing process, it becomes difficult to handle the electro-optical panel. In addition, since the transparent adhesives 30 tend to accidentally stick onto the outer surface of the transparent substrates 28 and 29, the electro-optical panel produced tends to be defective.